1. Field of the Invention
The present invention relates to a vehicle brake device for applying a brake force to a vehicle.
2. Discussion of the Related Art
Heretofore, as one example of vehicle brake devices that apply a brake force to a vehicle, there is known a hybrid vehicle brake device described in, for example, JP2012-16984 A. In the vehicle brake device, an input piston and a master piston are held to be separated with a predetermined space therebetween. Then, the moving amount of the input piston is detected, a demand brake force is calculated from the moving amount of the input piston, and a demand friction brake force is calculated by subtracting a regenerative brake force from the demand brake force. A servo pressure that is generated based on the demand friction brake force by the cooperation between an accumulating section (accumulator) and a linear valve is applied to a master cylinder, and hence, the master piston is moved to generate a master pressure. The master pressure is applied to wheel cylinders, whereby a friction brake force depending on the master pressure is generated.
In the vehicle brake device described in the Japanese application, there is a possibility that the input piston contacts the master piston when a brake pedal is stepped on quickly. When the input piston contacts the master piston, a stepping force from the input piston, in addition to the aforementioned servo pressure, acts on the master piston. This results in generating a master pressure exceeding the master pressure that is to be generated in dependence on the demand friction brake force.
While an ABS (antilock brake system) is in operation, the slipping of wheels is prevented by regulating the master pressure with the regenerative brake force set to zero. Heretofore, an inferred master pressure has been calculated from the moving amount or the like of the input piston, and the ABS has been controlled based on the inferred master pressure. However, as aforementioned, since an excessive master pressure is generated when the input piston contacts the master piston, deviation takes place between an actual master pressure and the inferred master pressure, hindering the control of the ABS. If the contact of the input piston with the master piston is inferred, such can be utilized in inferring the master pressure. Then, if it is done to accurately infer respective master pressures that are generated respectively when the input piston and the master piston are held in a separation state and a contact state, it becomes possible to enhance the performance in the brake control by the ABS or the like.